Weird bedtime quirk? Or something else?

For the past 4 or 5 nights, every time we put our baby girl to bed (around 7:30) she wakes up fussing or crying almost exactly an hour later. My husband is the pro at soothing her back to sleep, so he goes in, works his magic, and she's fine for about 5 hours, until she needs a bottle. But it's like CLOCKWORK! We even anticipated it tonight, and sure enough. She woke up an hour after we put her down. What is this?